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Zhang X.-Y.,Xian Shiyou University | Bi Z.-Y.,National Petroleum and Gas Tubular Goods Engineering Technology Research Center | Gao H.-L.,Xian Shiyou University | Niu H.,National Petroleum and Gas Tubular Goods Engineering Technology Research Center | Xu X.-L.,Xian Shiyou University
Journal of Iron and Steel Research | Year: 2014

The pipeline steel with the excellent deformability is a new type pipe structure material, for preventing the any pipe fracture due to plastic deformation by ground movement (such as earthquakes, landslides or permafrost region, etc) based on the strain-based design theory. The strain-aging embrittlement behavior of X80 pipeline steels with excellent deformability (PSED) was investigated by microscopic analysis and mechanical properties testing. The results indicated that strain-aging can induce the embrittlement behavior of X80 pipeline steel. Both strength and hardness of the PSED can be increased with the aging temperature, while ductility and toughness will be decreased. The strain-aging embrittlement mechanism of pipeline steel is the interaction of interstitial and dislocation. The strain-aging tendency of PSED is lower than that of ordinary X80 pipeline steel. The probable reason is the lower solution of carbon and nitrogen atoms, and the lower dislocation density in ferrite phase of dual-phase microstructure. Source


Zhang X.-Y.,Xian Shiyou University | Zhang X.-Y.,National Petroleum and Gas Tubular Goods Engineering Technology Research Center | Gao H.-L.,Xian Shiyou University | Gao H.-L.,National Petroleum and Gas Tubular Goods Engineering Technology Research Center | And 3 more authors.
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2014

The deformation and fracture behaviors of the X80 pipeline steel with excellent deformability were investigated by optical microscope and scan electronic microscope (SEM). The results indicate that plastic deformation is preferentially occured in ferrite during the deformation process for the experimental steel with dual-phases microstructure of bainite and ferrite. With the increase of the amount of plastic deformation, the morphology of the dual-phases microstructure shows a more obviously orientated distribution along the direction of applied force. Usually, the nucleation of crack in dual-phases microstructure has three typical ways such as inclusion nucleation, phase interface nucleation and nucleation in the matrix of ferrite or bainite. The propagation of cracks is related to the stress state of the steel. When the stress is low, the propagation of crack is mainly occurred in ferrite, and when the stress is high, the crack can propagate through the bainite phase. Finally, the deformation and fracture model of the dual-phases pipeline steel is established based on the studies above. Source

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